Our characterization of the Pten null prostate cancer model makes a compelling case that the mutant mouse mimics key features of human prostate cancer development and is a suitable model for investigating the cell- of-origin and cancer stem cells in prostate adenocarcinoma. The goal of this grant application is to test the hypothesis that a specific prostatic cell type is sensitive to the oncogenic transformation and therefore serves as the cell-of-origin of prostate cancer. To the advantage of these investigations, prostate cancer initiation and progression in the Pten mouse model is predictable within a condensed frame, thereby permitting a rapid and systematic study of the cellular, molecular and genetic events linked to tumor development. The Pten model also responds to hormone ablation therapy and develops hormone refractory prostate cancer (HRPC) following prolonged androgen depletion. We will first decipher the prostate epithelial stem-progenitor cell hierarchy under normal physiological conditions and then use this hierarchy map to identify cancer stem cells in the murine prostate cancer models and human prostate cancer samples (Aim 1). We will further address the cellular and molecular basis of HRPC. In particular, the link between androgen-independent growth and cancer stem cells will be carefully examined. With characterized cancer stem cells in hand, we will then investigate the molecular mechanisms underlying prostate cancer stem cell development, including pathways controlling stem cell self- renewal and differentiation, and test the effects of small pathway-specific inhibitors on cancer stem cells and HRPC development (Aim 2). We expect that the identification and functional characterization of both the cell- of-origin of prostate cancer as well as dysregulated signaling pathways will provide essential information for improved detection, diagnosis, and therapy of this disease. Although focused on prostate cancer, the studies outlined here and the mechanisms elucidated in this proposal will be broadly relevant, since PTEN is expressed in all cell types in the human body and PTEN mutations are observed in a variety of human cancers. PUBLIC HEALTH RELEVANCE: Despite its enormous impact on male health, the molecular mechanisms underlying the pathogenesis of prostate cancer remain unsolved. A central focus of this application is to characterize the prostate cancer stem cells and to test whether altered stem cell properties may contribute to prostate cancer development and hormone refractory prostate cancer development. This will help in understanding the origin of the disease and provide rationales for novel, stem cell-targeted treatment.